A {Co^III₂Dy^III₄} Single-Molecule Magnet with an Expanded Core Structure

The coordination cluster compound [CoIII2DyIII4(OH)2(ib)8(bdea)2(NO3)4(H2O)2]·2MeCN (1) self-assembles in a high-yield reaction of cobalt(II) isobutyrate (ib) with Dy(NO3)3·6H2O and N-butyldiethanolamine (H2bdea) in air. The Ci-symmetric {CoIII2DyIII4} core fragment features two {CoDy2(μ3-OH)} triangles, joined by one of their Dy sites via μ-O and μ-carboxylate bridges. This results in a flat zigzag metal skeleton, in contrast to previously reported hexanuclear {Co2Ln4(μ3-OH)2} clusters, namely, exhibiting a more condensed combination of two {CoLn2(μ3-OH)} triangles that form a Dy4 rhombus. According to ac susceptibility measurements, this rearrangement in 1 reduces quantum tunneling of the magnetization and hence pushes up the onset of pronounced out-of-phase signals at zero bias field to 14 K, a significant change vs the more condensed {Co2Dy4} structures. As intermolecular interactions between coordination clusters in the solid state are well-known to also influence SMM features, comparative Hirshfeld surface analyses are also presented.